Radar Test Research Articles

A new explosive method for soil improvement

A highway was constructed in Jiangxi Province, China, through a mountainous area. Some sections of the highway went through valleys where a soft clay layer 6–8·5 m deep was encountered. A new explosive method was developed and adopted for this project. The method uses the energy of the explosion to remove the soft clay and replace it with crushed stones. Explosive charges are placed in the soil to be improved according to a specific pattern. Crushed stones are piled up next to the area where the charges are installed. The explosion creates cavities in the soil and causes the pile of crushed stones to slide into the exploded area. The detail of the method and its application to the highway project are described. The effectiveness of the method is evaluated using borehole exploration, plate load tests and groundprobing radar tests.

GPS and GIS Assisted Radar Interferometry

Error in radar satellite orbit determination is a common problem in radar interferometry (INSAR). For example, when we try to locate a radar test site with known geographic coordinates using the geocoding information in SLC (the latitude and longitude of the four image corners), the location is well away from the true position. Another example is when there is a significant disturbance in the differential INSAR result, we sometimes are not sure whether it is from ground deformation or atmospheric heterogeneity. Even after these are corrected, we need to export the INSAR results to a GIS format so that they can be overlaid as layers over orthophotos and mine plans (in the case of mining subsidence) in order to interpret the results. Therefore, it is proposed to use both GPS and GIS to assist radar interferometry. Results are presented with an application to monitoring subsidence due to underground mining southwest of Sydney, Australia.

A new explosive method for soil improvement

A highway was constructed in Jiangxi Province, China, through a mountainous area. Some sections of the highway went through valleys where a soft clay layer 6–8·5 m deep was encountered. A new explosive method was developed and adopted for this project. The method uses the energy of the explosion to remove the soft clay and replace it with crushed stones. Explosive charges are placed in the soil to be improved according to a specific pattern. Crushed stones are piled up next to the area where the charges are installed. The explosion creates cavities in the soil and causes the pile of crushed stones to slide into the exploded area. The detail of the method and its application to the highway project are described. The effectiveness of the method is evaluated using borehole exploration, plate load tests and groundprobing radar tests.

A continuum of gravity waves in the Arecibo thermosphere?

Previous incoherent radar studies at Arecibo Observatory, Puerto Rico have demonstrated that ∼1–3% electron density “imprints” of internal gravity waves are routinely present in the Arecibo thermosphere (∼118–500 km). A special radar technique involving photoelectron‐enhanced plasma waves (PEPWs) was used for these observations. Recently, it was discovered that the trails of the gravity waves can be detected in standard incoherent scatter power profiles when properly filtered. This result was validated using simultaneous PEPW observations. This new development opens up the possibility of monitoring thermospheric gravity waves day and night. Preliminary studies indicate that gravity waves are continually propagating through the Arecibo thermosphere, and that “sets” of waves separated by approximately 20–60 min are typically present. With the aid of additional radar tests, it may be possible to unlock Arecibo power profiles recorded over the past 30 years for gravity wave studies. The precise origin of the waves is currently unknown.

Profiles of floating ice in Arctic regions using GPR

Geophysical crews have been collecting seismic data on the Arctic Coastal Plain for over 40 years. Most work is performed during the winter months to avoid environmental damage to the tundra. Seismic crews routinely operate over frozen lakes as well as on first year sea ice, and data collection may begin as soon as the ice is strong enough to support the equipment. Traditionally, the safe-bearing capacity of ice has been related to a minimum thickness and a subjective determination of the condition of the ice. This criterion has been established through years of experience and, for the most part, it has been quite successful. Ice conditions are monitored throughout the winter by drilling at designated intervals. This results in accurate thickness data at the collection points but does not provide any information between the points. Ice thickness by itself is not a good indication of ice strength. It is possible to have an ice sheet that is several feet thick and have near zero strength. However, flexural strength may be estimated when ice profiles are used in conjunction with other data. In an effort to obtain continuous profiles of the ice-water interface, a series of ground-penetrating radar (GPR) tests were performed. A GPR system was tested on lake ice as well as sea ice. In both cases, the bottom of the ice could be imaged. Radar profiles are normally displayed on a time scale. To convert the time scale to ice thickness, it is necessary to calculate the relative permittivity of the ice sheet. This is easily accomplished in the field. First year sea ice is a very complex mixture of ice, brine, and air. As the surface temperature of sea ice drops below freezing, small disks and needles of pure ice, termed frazil ice, form on the surface …

A DSP-Based Mixed-Signal Waveform Generator

As it currently stands, waveform generators are being employed in many diverse areas, such as radar applications, communication systems, simulation, and testing. There is considerable interest in exploring the beacon of opportunity posed by using digital signal processor (DSP)-based systems to replace costly and inadequate conventional waveform generators. The availability of high performance DSPs allows for the design of highly flexible equipment capable of real-time processing. The arbitrary waveform generator introduced in this paper consists of a DSP, a FIFO memory, a video palette, and a PC interface. A program running on the PC creates a digital representation of a waveform according to user parameters and sends it to the DSP's RAM. The DSP algorithmically converts the digital representation to a point-by-point representation of the desired analog signal. The data points are sent to the FIFO buffer, which latches the data to a video palette that serves a three-channel digital-to-analog converter. The system employs a high-speed serial port interface to communicate with a PC, to allow for readily programmed signals. In addition to the production of traditional signals, such as sinusoids and squarewaves, a mathematical tool known as splines is employed to aid in the development of customized arbitrary waveforms. Finally, a picture of our new device is presented in the paper.

Target Simulator to Calibrate Wideband Radar in Measuring the Internal Layers of the Greenland Ice Sheet

We developed a hardware target simulator for measuring the system response and testing of an airborne wideband radar that operates over the frequency range 600-900 MHz to map the near-surface internal layers in glacial ice. It uses optical and microwave delay lines for evaluating and optimizing the performance of the wideband radar in the continental United States without expensive field trips to polar regions and can be used to test the radar without interfering with commercial wireless devices and television stations. The target simulator replicates the feed-through signal between the transmit and receive antenna, as well as reflections from the air-firn interface and the internal layers of the ice sheet, which are spaced about 50 cm apart. This is because the measured radar resolution is about 60 cm in free space and can map layers with about 50-cm resolution in firn. We simulated the internal layers by incorporating a feedback loop with a short delay line. The target simulator is being used for testing and evaluation of the radar in the laboratory and for in-flight testing of the radar.

Hybrid Analog–Digital Variable Fiber-Optic Delay Line

A variable fiber-optic delay line (VFODL) is introduced that, to the best of the authors' knowledge, is the first time that a hybrid analog-digital VFODL is proposed to solve the dilemma of efficiently enabling many settable and long-duration time delays together with continuous and short time delays. In essence, this VFODL can provide near-continuous high-resolution time generation across an entire long-time-delay band. The VFODL is based on the concept of cascaded wavelength-sensitive and wavelength-insensitive time delays. A proof-of-concept VFODL built demonstrates near-continuous 0.5-ps-resolution time-delay control across an entire 25.6-ns time-delay band generating a total of 51 200 measurable time-delay bins. The experimental VFODL also gives a 4.95-dB total optical loss and a 1-ms time-delay control-setting speed. The proposed VFODL can be used in applications such as radio frequency photonic signal processing and radar testing.

Reliability of Radar Inspection for Detection of Pavement Damage

ABSTRACT Ground Penetrating Radar based analysis of road pavement is actually performed by many agencies involved in road management. The radar image interpretation is the most difficult step for the researcher to overcome. Software assisted processes have usually such a low reliability, that a road pavement engineer advisor is needed. The main aim of this paper is to assess the reliability of an optimal signal processing algorithm for pavement inspection. The algorithm is based on signal computing time delays. A threshold analysis of the error is carried out to check any damage and, subsequently, if damage is predicted, a second threshold analysis, subsequently points out its expected nature. This paper examines the experimental survey that has been performed both in laboratory and on road. The results show a good performance of the numerical algorithm and electronic equipment assessing the reliability of the procedure. It is also implemented the Neyman-Pearson radar test. The Receiver's Operating Characteristic is computed in different numerical configurations. The proposed system demonstrates a significant performance as the probability of false alarm is always lower than 20 per cent. In this sense the methodological approach can be reasonably considered to be reliable. In conclusion the experimental outcomes show that after calibration the proposed procedure makes it possible to diagnose many damages of flexible pavement. Moreover the class of damage respect to the three main classes, as defined in the paper, can be identified reliably.

Application of sonic and radar tests on the piers and walls of the Cathedral of Noto

The authors applied systematically sonic tests, radar tests and other diagnostic techniques on the remaining walls and piers of the Cathedral of Noto. The experimental survey was carried out by the Laboratory of the DIS, Politecnico of Milan (Person in Charge: Prof. Binda, Prof. Baronio) in collaboration with the designers (Ing. R. De Benedictis, Arch. S. Tringali) and the experts working on the reconstruction. The Prefettura of Siracusa founded the research. The right aisle and most of the dome of the Cathedral collapsed in 1996. The aim of the research was to verify the state of damage and the possibility of conservation of the walls and piers in view of the reconstruction of the damaged part of the Cathedral. Furthermore, the sonic tests were used to control the effect of grout injection used as a possible technique for repair of the damaged masonry (Proceedings of the Conference on Nondestructive Evaluation of Civil Structures and Materials, Boulder, Colorado; (1992) 329; Proceedings of the Sixth Conference on Structural Faults and Repair, 3 (1995) 195). In the following the results will be reported and the reliability of the tests will be discussed as it was confirmed by the use of other complementary diagnosis techniques (Proceedings of the Sixth International Conference on Structural Studies, Repairs and Maintenance of Historical Buildings, STREMAH 99, Dresden, Germany, (1999) 323).

Sub-surface radar testing of concrete: a review

The background and current state of the art of radar testing of concrete is briefly reviewed. This encompasses developments of equipment, procedures, applications, analysis, interpretation and presentation of results. There has been substantial progress in all these areas over the past ten years and reference is made to recent and ongoing research. Key documents from the literature are identified including authoritative guidance reports on practical usage.

Deficiency Analysis of As-Built Database to Enhance a Pavement Management System

The ability to systematically collect and record as-built data for pavement layers benefits highway departments in many aspects. A well-established database of as-built pavements provides a tool for maintaining an up-to-date corporate record of the physical pavement structures, keeping track of unit construction costs, and reducing the amount of pavement excavations during pavement investigations. A reliable as-built database also provides inputs for falling weight deflectometer analysis and calibrating pavement performance models in pavement management systems (PMSs). A task within the development of the second-generation PMS for the New Jersey Department of Transportation is to review and analyze the existing pavement as-built database for completeness and quality. A computer program was developed to scan and categorize the as-built data into five status levels: complete, partially complete—missing original construction data, partially complete—missing recent rehabilitation data, questionable data, and no data. The results of this analysis can be used to recommend improvement for the data-collection process and to guide further investigations, such as coring and ground penetration radar tests. The general approach used in the analysis is described, data status levels are defined, results for distribution of the pavement as-built data are provided, and the significance of the analysis for PMSs is discussed. Recommendations for improving completeness and quality of the pavement construction history database also are provided.

Signatures of resonant and non-resonant scattering mechanisms on radar images of internal waves

The results of two polarization airborne radar imagery tests of the ocean surface obtained during the JUSREX'92 experiment are presented. It is shown that the traditional composite surface model with small-scale 'Bragg' waves superposed over larger gravity waves can not explain either the contrasts of internal wave surface manifestations in conditions of a stable atmospheric boundary layer at low grazing angles (LGA), or the apparent difference between the images obtained at different polarizations in unstable atmospheric conditions. We attribute this discrepancy to the presence of mesoscale steep waves, which produce non-resonant scattering and make different relative contributions to the total cross sections for the two polarizations. The possibility of distinguishing between surface manifestations of atmospheric and oceanic origin is also discussed.

Radar Testing of a Masonry Composite Structure with Sand and Water Backfill

As part of an ongoing program into the noninvasive geometrical characterization of masonry arch bridges, a laboratory study of radar propagation through masonry has been undertaken. A 2.4 m long × 1 m wide × 1.5 m high experimental test rig was built in the laboratory with brick walls on three sides and a wooden gate on the fourth narrow side. The objective was to construct a composite test rig that would replicate certain of the environments that ground-penetrating radar might encounter when being used to test a masonry arch bridge. Tests were undertaken using 500, 900, and 1,000 MHz bow-tie antennas with the masonry box filled with fresh water and then saline water with different concentrations of sodium chloride. Further tests were undertaken with the masonry box filled with dry sand and wet sand. Finally the test rig was modified to simulate a composite masonry structure and tests were performed both on the hollow- and sand-filled models. The results from this work are reported herein indicating the r...

Dielectric properties of concrete and their influence on radar testing

Sub-surface radar is becoming increasingly popular as an inspection method. Interpretation can be enhanced if uncertainties about the dielectric properties of the concretes under investigation are removed. The need for reliable data to identify possible variations of the dielectric properties of different concrete mixes and their condition on site has led to a systematic laboratory based experimental programme under the auspices of a major European Commission (Brite-Euram III Framework 4) funded project. Some key results from this recently completed work are presented in this paper with practical implications related to field surveys of structural concrete.

Modeling and Simulation of Computerized Tomography Systems

The field of Computerized Tomography (CT) has revolutionized medical imaging and has been ap plied to the diverse fields of radio astronomy, elec tron microscopy, geophysics, stress analysis, radar, and nondestructive testing. Computer simula tion has played an integral role in the development of CT systems and algorithms. This article pro vides an overview of CT and the tools used to model and simulate CT systems, and demon strates the evaluation of a novel Localized CT (LCT) technique through simulation. The key features of the discrete wavelet transform are reviewed as they relate to the development of LCT algorithms. The Shepp-Logan head phantom is presented and utilized in the simulation and evalu ation of the proposed LCT technique.

First testing of a volcano Doppler radar (Voldorad) at Mount Etna, Italy

A medium‐power (1 kW) Doppler radar of limited weight (110 kg) and working in the UHF band has been developed for active remote sensing of volcanic eruptions. Named Voldorad, this radar is designed to monitor eruptive activities of variable magnitude at medium distance range (∼0.5–5 km), in any weather condition, and fills the gap between low‐ and high‐power radar or sodar systems previously tested on volcanoes. Voldorad was operated for the first time during an eruption of Mt. Etna on October 11–12, 1998. Doppler spectra recorded at 1 km distance from the vent reveal powerful echoes during the eruption paroxysm (lava fountains), which gradually decreased along with declining activity. An average vertical velocity of 80–87 m s−1 is inferred for the eruptive jets.

NDE of masonry structures: use of radar tests for the characterisation of stone masonries

Ground penetrating radar is being used as a survey tool to study stone and brick masonries. The aim of the research is to produce guidelines for a technical procedure for the acquisition and interpretation of radar traces to detect inclusions, voids and other defects, the effectiveness of repair, the characteristics of leaves in multiple-leaf walls and to find the presence of moisture in a stone masonry wall. This paper shows first results of in situ tests carried out on historic buildings.

VXI based breadboard module use

Plug-in VXI based breadboard modules are an excellent solution to achieve a lower costing, time and hardware saving test bench. These breadboard modules are equipped with built-in VXI bus interface circuitry and a breadboard area for creating a design to suit your test needs. A prime example for the use of this capability was demonstrated on a recent radar system test bench created to test many unique Units Under Test (UUTs) previously tested on separate test benches. A single breadboard module design replaced the dedicated interface and control hardware within the many test benches and test fixtures previously used to test the individual UUTs. This paper presents some design considerations and techniques implemented as part of this VXI breadboard module that can be useful when creating a VXI breadboard design. It also addresses the inherent built-in test capabilities provided by the module in conjunction with the techniques presented in the paper.

Nonlinear nonadaptive space–time processing for airborne early warning radar

The paper deals with the cancellation of clutter echoes in modern airborne early warning radar systems equipped with digital beamforming. Performance is compared of the following two-dimensional filters that operate in the angle and Doppler frequency domains: (i) fully adaptive linear filter, (ii) partially adaptive linear filter, (iii) linear filters with displaced phase centre antenna weights and with fixed Chebyshev tapering, and (iv) the recently conceived nonlinear filter which takes the minimum among the outputs of few linear filters that process the same radar signals with properly selected weights. The fully adaptive filter requires the highest computational burden and a large region of homogeneous clutter to estimate the clutter covariance matrix. Filter (ii) alleviates these drawbacks at the expense of a reduced cancellation. Filters (iii) are the simplest but offer limited performance. The nonlinear filter is a compromise solution, since its computational requirement is slightly higher than filter (iii), but much less than (i) and (ii), and its performance is comparable to filters (i) and (ii). Moreover, since it requires a limited form of adaptation, it shows much higher robustness to nonhomogeneous clutter. Further, the filters are compared against the live data recorded by the experimental radar adaptive array flight test equipment of NRL. The set of real data, which relates to the sea-to-ground transition, allows demonstration of the robustness of the new nonlinear detector to nonhomogeneous conditions.